Specifically, it is already known to continuously monitor the pressure inside the tires of a vehicle. These pressure measurements (possibly corrected as a function of the temperature and of the ageing of the tire or of any other parameter) are processed by computer and an alarm signal is emitted when the pressure of a tire is abnormal. The computer processing the pressure measurements can be installed on the wheel itself or at any appropriate place of the vehicle.
The pressure measurements are carried out by a specific sensor associated with each of the wheels. The pressure measurement associated with a code identifying the sensor is sent to a remote computer by this sensor. Of course, it is necessary for the computer to know how to attribute this identifying code to a sensor position on the vehicle. Thus after processing, the computer must be capable of saying that the pressure measurement associated with the identifying code X originates from the front right wheel (for example). To do this, it is necessary for the computer to learn the position, on the vehicle, of the sensor and its identifying code.
This learning can be performed manually. For example, the computer is placed in learning mode and requests the codes of each of the pressure sensors in a preset order. This learning method is however relatively slow. Furthermore, it must be repeated with each change of tire and has the drawback of compelling the driver to enter data into the computer of the vehicle. If the driver forgets to store the new code in memory after a change of tire, there is a risk of error in the position of a wheel exhibiting an abnormal pressure. This may have serious consequences.
It would appear appropriate to carry out this learning of the position of the wheels, automatically, while the vehicle is moving.
To do this, the following physical principle is used: when cornering, the inside wheels turn less quickly than the outside wheels.
However, trials carried out while allowing for the centripetal acceleration of each wheel show that deviations of speed between right and left wheel are of the order of 1 to 10% of the measured value (acceleration).
Knowing that standard accelerometers making it possible to measure the centripetal acceleration of the vehicle have a resolution of 1%, noise of ±10%, an error of ±15% and exhibit drifting with temperature and with time, it seems impossible to use the measurement of the centripetal acceleration of each wheel by using standard accelerometers, to determine by direct comparison which wheel is turning least quickly.
It is of course possible to use more accurate accelerometers, but the accuracy of measurement required here involves the use of very expensive and generally very fragile accelerometers. This solution is inapplicable in the automotive environment.
The aim of the invention is therefore to determine automatically the position of the right and left wheels of a vehicle by using standard accelerometers.
For this purpose, the present invention relates to a method of automatic location of the right and left wheels of a motor vehicle of the type comprising a step of automatic measurement of the centripetal acceleration of a wheel, said method being characterized in that it consists in comparing the theoretical centripetal acceleration of a wheel in a straight line with the measured centripetal acceleration of this same wheel when cornering for a given vehicle speed, and for a given steering wheel angle, so as to determine whether said wheel is on the right or on the left of the vehicle.
Thus, by comparing the acceleration of one and the same wheel in a straight line and when cornering, problems of dispersion of the accuracies of the various acceleration sensors, one with respect to another, are circumvented.
More especially, the present invention relates to a method of automatic location consisting firstly in:                a)—measuring the vehicle's steering wheel angle T and when this steering wheel angle is substantially zero (vehicle in a straight line),        b)—measuring the centripetal acceleration Ai of each of the wheels of the vehicle with the aid of a sensor associated with each of the wheels, and        c)—determining a correction coefficient ki for each of the wheels according to the following law:Ai=KiV2  (1)         where Ai is the straight-line centripetal acceleration measured on wheel i, and V is the speed of the vehicle,and consisting, subsequently, when the vehicle is cornering:        d)—in measuring the centripetal acceleration while cornering Aiv of each of the wheels,        e)—in forming the difference in acceleration Δi between the theoretical acceleration in a straight line Ai for a given wheel i and a given speed V, and the acceleration measured while cornering Aiv of this same wheel and at this same speed,Δi=Aiv−Ai, that is to sayΔi=Aiv−KiV2  (2)        f)—in forming the product of this difference Δi times T the angle of the steering wheel,(Aiv−KiV2)×T  (3)        g)—in determining the sign of this product, as a function of a chosen convention, namely; negative steering wheel angle if cornering to the left (or the converse), and        h)—deducing therefrom for each of the wheels its location on the left or right side of the vehicle.        
Advantageously, a correction coefficient is calculated for each wheel when the vehicle is in a straight line. This makes it possible to intercompare the measurements made by the sensors on various wheels while circumventing, here again, errors and inaccuracies among the various sensors.
Advantageously, the present invention makes it possible to employ standard sensors and to obtain results with an error of less than 1%.
Advantageously, again by fixing a convention for the representation of the steering wheel angles (for example the negative steering wheel angles correspond to a cornering of the vehicle to the left), and by simply determining the sign of the following product:
 (Aiv−KiV2)×T
where Aiv is the measurement of the acceleration of wheel i while cornering, KiV2 is the theoretical acceleration of wheel i in a straight line, and T the algebraic value of the steering wheel angle, it is possible to deduce therefrom whether the wheel i is a right or left wheel of the vehicle.
Specifically, assuming that the convention for measuring the steering wheel angle establishes that a cornering to the left has a negative angle, then when the vehicle is turning to the left, we obtain T<0. When a vehicle is turning to the left, its left wheel has a lower speed than this same left wheel on a straight line. Likewise, the acceleration of the left wheel when cornering is less than the acceleration of this same left wheel on a straight line. Therefore, the difference Δi between the acceleration measured while cornering and the theoretical acceleration in a straight line is less than 0. The product of T times Δi is therefore positive.
If for this same convention for measuring the steering wheel angle the product T times Δi is negative it is because the wheel i is a right wheel.
Thus, for the established convention for measuring the steering wheel angle (left=negative) the sign of the product T×Δi indicates directly that wheel i is on the right when it is negative and that wheel i is on the left when it is positive.
Advantageously, to improve the accuracy of the locating of the right and left wheels, it is possible to redo the determination of the right and left wheels a number of times and to confirm it only when the same location has been found several times, for a given wheel.
Advantageously again by summing a plurality of Δi of one and the same wheel and comparing this sum with all the sums of the other wheels (choosing the negative steering wheel angle preset for cornering to the left), the largest two sums obtained correspond to the left wheels of the vehicle.